There are many applications where it is desired or necessary to use an antenna to radiate electromagnetic waves. In particular, some applications require that the electromagnetic waves be emitted with a specified directivity.
For example, in radar applications, it is advantageous for a certain directivity to be used to emit electromagnetic waves in order to correlate the electromagnetic waves reflected off of and received at an object to the position of the object. Cellular radio is another application where a certain directivity is desirable for the emission of electromagnetic waves. For example, a plurality of radio antennae are mounted on radio towers of the cellular radio system providers that each cover a specific area of the radio cell serviced by the particular radio tower. For example, three antennae may be provided, each of which has an approximately 120° angle of aperture.
In radar applications in particular, the direction in which the electromagnetic waves are emitted must be varied to be able to monitor a relatively large spatial area using the radar. Movable or swivel-mounted antennae are used, for example.
Such antennae require a mechanical system that allows the antenna that is mounted thereon to move in an appropriate way.
What are generally referred to as phased array antennae are also known today, where the antenna radiation pattern is electronically steerable. Phased array antennae are composed of a plurality of transmitting elements (array) that are fed from a common signal source. To steer the antenna radiation pattern of such a phased array antenna, the individual transmitting elements of the phased array antenna are controlled by a suitably phase-shifted signal. As a result, the individual emitted electromagnetic waves are superimposed on one another in the desired direction, producing a constructive interference, thereby forming a maximum of emitted energy in the desired direction.
Such phased array antennae include a phase shifter and an attenuator in order to individually adjust the phase and amplitude for each of the transmitting elements.
An exemplary phased array antenna is shown in FIG. 1. The phased array antenna of FIG. 1 has four transmitting elements S1-S4 that are each coupled to a common signal source FN (also referred to as feed network). An attenuator V1-V4, as well as a phase shifter P1-P4 disposed in series relative thereto are located between signal source FN and the individual transmitting elements.
German Patent Application DE 102010040793 (Al), for example, discusses an antenna that is suited for use in radar applications.